1. Field of the Invention
The present invention relates to stepper motors generally and, more particularly, but not by way of limitation, to a novel linear stepper motor, a fixture for the magnetization of the shaft thereof, and methods of use and manufacture.
2. Background Art
Some linear stepper motors convert rotary motion to linear motion by mechanical means such as through the use of a threaded nut and lead screw. Conventional linear motors that directly transfer electromagnetic energy in the stator poles to linear movement of a shaft typically employ toothed structures or have relatively complicated slide/stator arrangements. In either case, the manufacture of such motors is relatively expensive and the motors typically have high parts counts.
A problem resides in producing a linear motor with a smooth shaft with alternating N and S poles. One technique is to glue together cylindrical segments of N and S magnets. That technique, however, is time consuming and results in a somewhat weak structure. Another technique is to roll a cylinder of ferromagnetic material over a flat plate orthogonal to a series of alternating N and S magnetic strips. This technique is somewhat clumsy and suffers from the fact that the resulting magnetized shaft is of fairly weak magnetic strength.
Some conventional motors are described in the following patent documents:
U.S. Pat. No. 3,867,676, issued Feb. 18, 1975, to Chai et al., and titled VARIABLE RELUCTANCE LINEAR STEPPER MOTOR, describes such a motor that has toothed structures on the coils and on the linear member. The novelty of the patent appears to reside in the arrangement of the coils and the manner in which they are energized.
U.S. Pat. No. 4,198,582, issued Apr. 15, 1980, to Matthias et al., and titled HIGH PERFORMANCE STEPPER MOTOR, describes, in part, a variable reluctance linear stepper motor in which both the stator and the slider have nonmagnetic materials arranged therein such that flux leakage is reduced.
U.S. Pat. No. 4,286,180, issued Aug. 25, 1981, to Langley, and titled VARIABLE RELUCTANCE STEPPER MOTOR, describes, in part, such a motor having helically toothed stator and slide structures, the respective widths of the teeth having a predetermined relationship.
U.S. Pat. No. 4,408,138, issued Oct. 4, 1983, to Okamoto, and titled LINEAR STEPPER MOTOR, describes a linear stepper motor having toothed structures on the stator and on the slider. Coil-wound salient poles are provided on the slider. The novelty of the patent appears to reside in the arrangement of rollers and rails disposed between the stator and the slider
U.S. Pat. No. 4,607,197, issued Aug. 19, 1986, to Conrad, and titled LINEAR AND ROTARY ACTUATOR, describes a variable reluctance linear/rotary motor in which the armature has axial rows of teeth radially spaced around the surface thereof. Selective energization of stator windings provides linear, rotary, or both linear and rotary motion of the armature.
U.S. Pat. No. 4,622,609, issued Nov. 11, 1986, to Barton, and titled READ/WRITE HEAD POSITIONING APPARATUS, describes a variable reluctance positioning device having toothed structures on facing surfaces of the stator and the armature and with coils placed on the armature.
U.S. Pat. No. 4,695,777, issued Sep. 22, 1987, to Asano, and titled VR TYPE LINEAR STEPPER MOTOR, describes such a motor having toothed structures on the stator and on the slider, the toothed structures on the stator being on coil-wound salient poles. The toothed structures bear a predetermined relationship therebetween.
U.S. Pat. No. 4,712,027, issued Dec. 8, 1987, to Karidis, and titled RADIAL POLE LINEAR RELUCTANCE MOTOR, describes such a motor having a smooth double-helix stator shaft and a smooth laminated armature of alternate radial pole laminations and spacer laminations. This arrangement permits a balanced flux path and uses the stator and armature surfaces as slider bearing surfaces.
U.S. Pat. No. 4,810,914, issued Mar. 7, 1989, to Karidis et al., and titled LINEAR ACTUATOR WITH MULTIPLE CLOSED LOOP FLUX PATHS ESSENTIALLY ORTHOGONAL TO ITS AXIS, describes a variable reluctance actuator similar in pertinent respects to that described in the ""027 patent above.
U.S. Pat. No. 6,016,021, issued Jan. 18, 2000, to Hinds, and titled LINEAR STEPPER MOTOR, describes a variable reluctance stepper motor similar in pertinent respects to the motor described in the ""609 patent above. The novelty of the patent appears to reside in the method of forming the teeth
Accordingly, it is a principal object of the present invention to provide a permanent magnet shaft for a linear stepper motor that has a smooth, external peripheral surface.
It is a further object of the invention to provide a linear stepper motor that has low parts counts and is simple and economical to manufacture.
It is an additional object of the invention to provide a method of magnetizing a smooth shaft for a linear stepper motor that is quick and economical.
It is another object of the invention to provide a fixture for magnetizing a smooth shaft for a linear stepper motor.
It is yet a further object of the invention to provide a fixture for magnetizing a smooth shaft for a linear stepper motor that can be economically manufactured.
It is yet an additional object of the invention to provide such a stepper motor conventional coils each easily wound around a bobbin.
It is yet another object of the invention to provide such a stepper motor having a shaft that can rotate at any position at any time, whether or not the motor is on or off or the shaft is moving linearly.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.
The present invention achieves the above objects, among others, by providing, in a preferred embodiment, linear stepper motor, comprising; an annular stator structure; an axially extending, cylindrical, permanent magnet shaft extending coaxially through said annular stator structure; and said axially extending, cylindrical, permanent magnet shaft having a smooth external surface along a portion thereof with axially alternating N and S poles defined circumferentially in an outer periphery of said portion of said axially extending, cylindrical, permanent magnet shaft. The present invention also provides a method of magnetizing the shaft of such a motor and a fixture and method of manufacturing the fixture therefor.